12-6-2013 • Orlich MJ, Singh PN, Sabaté J et al.

Vegetarian Dietary Patterns and Mortality in Adventist Health Study 2

Background

Several studies have investigated the relationship between dietary factors and mortality. For instance nuts, fruit, cereal fiber, polyunsaturated fatty acids (PUFAs), ω-3PUFAs, green salad, Mediterranean dietary patterns, plant-based diet scores and vegetarian diets have been found to be correlated with reduced mortality. In contrast, high glycemic load, processed or red meat, eggs, potatoes and animal-based low-carbohydrate diets, among other dietary factors, have been associated with increased mortality.
Vegetarian diets have been linked to reduced risk for several chronic diseases, including hypertension [1,2], metabolic syndrome [3], diabetes mellitus [4,5] and ischemic heart disease (IHD)[6,7]. This could result in lower mortality, but mixed results on the relationship between vegetarian dietary patterns and mortality have been published.
This study aimed to evaluate the possible association of vegetarian dietary patterns with reduced mortality in the Adventist Health Study 2 (AHS-2), in a cohort of 73308 Seventh –day Adventists [8]. According to the reported intake of foods of animal origin, participants were divided into vegans (7.6%), lacto-ovo-vegetarians (eggs/dairy >1x/month, other meats <1x/mo, 28.9%), pesco-vegetarians (fish >1x/mo, other meats <1x/mo, 9.8%), semi-vegetarians (nonfish meats >1x/mo and all meats combined >1x/mo but not more than 1x/wk, 5.5%), and nonvegetarians (nonfish meats >1x/mo and all meats combined >1x/wk, 48.2%). Mean follow-up time was 5.79 (SD: 1.31) years, in which 2570 people passed away (6.05 deaths per 1000 person-years).

Main results

At baseline, vegetarian groups tended to be older, more highly educated, and more likely to be married, to drink less alcohol, to smoke less, to exercise more, and to be thinner.

Overall, all vegetarian diets combined showed a lower adjusted risk of death as compared to nonvegetarians (HR: 0.88, 95%CI: 0.80-0.97). The effect was stronger for men (HR: 0.82, 95%CI: 0.72-0.94) than in women (HR: 0.93, 95%CI: 0.82-1.05).

Vegetarian men had a lower risk for CVD mortality (HR: 0.71, 95%CI: 0.57-0.90) and IHD mortality (HR:0.71, 95%CI: 0.51-1.00), while women did not.

Pesco-vegetarians had reduced risk for all-cause mortality, IHD and other mortality (non-CVD, noncancer), as compared to nonvegetarians. Male pesco-vegetarians were at reduced risk for all-cause mortality, CVD mortality and other mortality, while women only for IHD mortality.
Lacto-ovo-vegetarians had significantly reduced risk for all-cause mortality, and men specifically for CVD mortality.
Vegans were at reduced risk for other mortality and male vegans for all-cause mortality, IHD mortality and CVD mortality.

Within the category of ‘other mortality’, vegetarians had a reduced risk of renal mortality (HR: 0.48, 95%CI: 0.28-0.82) and endocrine mortality (HR: 0.61, 95%CI: 0.40-0.92) Again, effects were strongest in men. Renal failure and diabetes mellitus were common in this category.

Adding BMI to the model in a sensitivity analysis only modestly affected the results.

Conclusion

Overall, vegetarian dietary patterns were associated with lower mortality, as compared to nonvegetarian diets. Some associations demonstrated a specific benefit for cardiovascular mortality. Effects were generally stronger in men than in women.

Editorial comment [9]

This study supports evidence that vegetarian diets are associated with improved health outcomes. However, although well-performed, an observational study cannot provide cause-and-effect evidence. Another limitation of this study is the large variety of diets consumed by those identified as vegetarians, and that no information is provided on the overall quality or quantity of the diet. In addition to or even stronger than achievement of beneficial health outcomes, religious, ethical or environmental beliefs may motivate somebody to decrease meat intake. These factors should all be considered when giving dietary advice. However, for most patients, the primary nutritional goal is to control calories and prevent weight gain. It may be more important to help patients follow more common features of diets associated with good clinical outcomes than to focus on whether to include moderate amounts of dairy, eggs, fish or even meat.